In an example, a method includes, at least one processor, in response to each of a plurality of requests, determining a halftone screen. Determining the halftone screen comprises encoding a signature pattern in the halftone screen, and halftone screens for different requests may be encoded with a different signature pattern. The halftone screen may be arranged such that, when applied to image data to provide a printed output, the pattern is discernible therein to provide a signature for the printed output.
Legal claims defining the scope of protection, as filed with the USPTO.
2. A method according to claim 1 further comprising transmitting each halftone screen to an entity identified in the request.
3. A method according to claim 2 further comprising encrypting each halftone screen and transmitting the encrypted halftone screen.
4. A method according to claim 2 further comprising storing an indication of each signature in association with an identity of each entity to which the halftone screen was transmitted.
5. A method according to claim 4 wherein storing the indication of each signature comprises securely storing the indication.
9. A method according to claim 1, wherein the halftone screen includes a matrix of threshold values that corresponds to the signature pattern.
10. A method according to claim 1, wherein applying the halftone screen to the image data includes associating a pixel of the halftone screen with a pixel of the image data, comparing a pixel value of the image data with a threshold value of the pixel of the halftone screen, and determining print instructions for the pixel of image data based on a result of the comparison.
13. A method according to claim 12 wherein accessing the halftone signature comprises accessing a pattern encoding the signature and determining, based on the digital sample, whether the printed image comprises the pattern.
14. A method according to claim 11 wherein the determining if the printed image contains the halftone signature comprises determining a fuzzy match which allows for randomisation introduced by the printing process.
16. Processing apparatus according to claim 15 in which the security module is to securely store an indication of the pattern.
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January 30, 2020
May 7, 2024
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